The invention relates to methods and devices for manipulation of small amounts of liquids on surfaces, preferably chip surfaces.
The term liquid, in the present text, includes among others liquids, mixtures, dispersions, and suspensions, as well as liquids, in which solid parts, for example, biological material, are located.
With the “lab-on-a-chip” technology existing at the earliest time, it is desirable to move a defined, small quantity of liquid to a defined analysis or synthesis point. The quantities of liquid are therefore, for example, in the range of pico-liters or milliliters. The analysis points often have only dimensions of a few micrometers or less on chips in the size of electronic semi-conductor elements.
The analysis of this type of quantities of liquid already is used today for analysis in biology (Ann Y. Fu et al., Nature Biotechnology 17, page 1109 and on (1999)). These methods are used, among other things, for inorganic reagents or organic material, such as cells, molecules, macromolecules or genetic materials, or in buffer solutions.
Thus, the movement and the reaction of defined volumes of small quantities of liquids are realized by means of micro-structured channels (for example, O. Müller, Laborwelt 1/2000, pages 36–38). Such channels, for example, are etched into the chip and are many micrometers deep or wide and generally capped. The movement takes place by means of electrokinetic (M. Köhler et al, Physicalische Blätter 56, Nr. 11, pages 57–61), mechanical or electrical pumps or capillary forces, respectively, in micro-structured channels.
High pump power is necessary, in order to move a liquid through these channels. Based on the sharp edges and narrow channels, cleaning after use is very difficult.
Should a liquid or material contained therein be analyzed on a specific surface, then often a chemically, physically, and/or biologically functionalized surface is used. In order to perform such analysis or synthesis at a good localized point, the functionalized area must be located within a channel and is thus difficult to make. With a corresponding functionalizing on a free surface without channel forming, on the other hand, an accurate localization of the liquid during the analysis is not warranted.